1. Field of the Invention
The present invention relates to a suspension system, and in particular, to an active suspension system capable of sensitively absorbing vibration generated when a vehicle runs on an uneven road and improving running stability.
2. Description of the Related Art
Many suspension systems commonly in use are classified as passive suspension systems. Passive suspension systems react to shocks, loads, and uneven terrain after the vehicle encounters them. Generally, passive suspension systems include struts, springs and resilient pads, and these systems are limited because they are unable to detect changing conditions and accordingly alter the suspension system before those conditions ultimately affect the ride and performance of the vehicle.
Active suspension systems have been designed to overcome some of the shortcomings associated with passive suspension systems.
FIG. 1 shows a prior art active suspension system. As shown in FIG. 1, the active suspension system includes a hydraulic pump 1 for generating and circulating hydraulic pressure, an oil tank 2 for storing oil, a proportional relief valve 3 connected to the hydraulic pump 1 and oil tank 2 for adjusting hydraulic pressure by releasing surplus oil to the oil tank 2, a manometer 4 for displaying present pressure level, an on/off valve 5 for controlling flow direction of the hydraulic oil, a vibration absorbing tank 6 for absorbing vibration generated when a vehicle runs on uneven road surfaces, a damper 7 operated by hydraulic pressure supplied by the hydraulic pump 1, an accelerometer 8 for sensing a vehicle speed, a coil spring 9, a height sensor 10 for measuring a height of a vehicle body, an amplifier 11 for amplifying signals received from the accelerometer 8 and the height sensor 10, an A/D converter 12 for converting the amplified analog signals into digital signals, a signal controller 13 for processing the signal with an algorithm, a D/A converter 14 for converting the digital signal from the signal controller 13, and an amplifier 15 for adjusting the analog signal received from the A/D converter 14 so as to properly control the on/off valve 5 and the proportional relief valve 3.
In this active suspension system, the oil is fed to the damper 7 through a hydraulic line by the hydraulic pump 1 actuated by the driving force of a motor. The hydraulic flow from the hydraulic pump 1 is monitored by the manometer 4 and if the hydraulic pressure level is higher than an optimal level, the relief valve 3 is opened so as to release the surplus oil to the oil tank 2.
Next, the hydraulic flow is directed to the damper 7 by the on/off valve 5 so as to be fed to the vibration absorbing tank 6 and cylinder chamber of the damper 7. The vibration absorbing tank 6 absorbs minute vibrations generated when the vehicle runs on uneven road.
The accelerometer 8 and the height sensor 10 respectively detect the vehicle speed and the height of the vehicle body and responsively produce electric signals. The amplifier 11 receives the electric signals and amplifies them to a predetermined range, then the A/D converter 12 converts the amplified analog signals into digital signals and sends the same to the controller 13. The controller 13 produces a damper control signal on the basis of the digital signal received from the A/D converter and sends the damper control signal to the D/A converter. The D/A converter 14 converts the damper control signal into a corresponding analog damper control signal. The analog control signal is amplified by the amplifier 15 and is then used for controlling the proportional relief valve 3 and the on/off valve 5.
The above active suspension system considerably improves shock absorbing performance. However, the active suspension system has drawbacks in that a great deal of electric power is consumed for operating the hydraulic mechanism.
To solve the above problem, another active suspension system is provided with an actuator mounted parallel with the shock absorber, and having a spring (See FIG. 2 and FIG. 3). The actuator is initially supplied with a hydraulic pressure of 50bar so as to lift the vehicle body, and in this case, a nitrogen tank absorbs road vibration by pressurizing or depressurizing therein.
However, the above suspension system also has shortcomings in that if the hydraulic mechanism malfunctions, the height of the vehicle body comes down as much as 100 mm. Furthermore, there is a limit to the size the nitrogen tank can be increased to in order to improve the vibration absorbing performance, and openings formed in the nitrogen tank cannot be adjusted such that the absorbing performance remarkably decreases.
The present invention has been made in an effort to solve the above problems of the prior art.
It is an object of the present invention to provide an active suspension system capable of improving shock and vibration absorbing performance.
It is another object of the present invention to provide an active suspension system capable of reducing electric power consumption as well as increasing ride stability.
To achieve the above objects, an active suspension system for an automotive vehicle of the present invention comprises a mono-tube shock absorber for passively absorbing impact from a wheel, an actuator formed around the mono-tube shock absorber, the actuator acting as a cylinder for the mono-tube shock absorber, a coil spring mounted around the actuator for assisting the mono-tube shock absorber and suspending the vehicle body, a servo amplifier connected to the actuator for adjusting hydraulic pressure, a servo valve connected to the servo amplifier for duty control by selectively activating the actuator, and an on/off valve electrically connected to the servo valve for selectively activating the actuator.